Forum Schedule Fall 2023

Fridays 3:45pm - 4:45pm BPB-217

Date Speaker Topic (click down-arrow to see abstract)
Sep 1 Matilde Signorini
Univ. of Florence
host: Daniel Proga
Reverberation Mapping: shedding light on high-redshift SMBH mass measurements, Broad Line Region physics and the H0 constant

Reverberation Mapping (RM) is an amazing technique that enables the measurements of Supermassive Black Hole (SMBH) masses beyond the local Universe. Understanding the formation and accretion history of SMBHs depends upon these measurements, but their execution at high redshift has posed significant observational challenges. I will discuss the campaign on SDSS J2222+2745, a lensed quasar at z=2.8, and how its characteristics can help us overcome many of these challenges. Furthermore, I will show how the high-quality data of the campaign allows us to directly model the Broad Line Region emission, which provides independent mass measurements, together with valuable insights into quasars physics.

I will also discuss an ongoing project in which the synergy of infrared Reverberation Mapping with spectroastrometry measurements can give us an independent estimate of the local H0 constant.

Sep 8 Jaehan Bae
University of Florida
host: Zhaohuan Zhu
Witnessing the formation of giant planets and their moons

With over 5,000 exoplanets discovered, it is clear that planet formation is a robust and widespread process. However, the astonishing diversity between observed exoplanetary systems suggests that environmental factors - the physical conditions present during birth of the planets - could influence the characteristics and architecture of the resulting planetary systems. The most direct way to test this hypothesis is to detect and characterize young planets at the time they are forming within their birth protoplanetary disks. The task of observing young, forming planets has long been very challenging, but it has finally become possible with increasingly powerful observing facilities and techniques. In this talk, I will (1) introduce recent high-resolution observations of protoplanetary disks, (2) show how state-of-the-art observations, along with theories and numerical simulations, can help us better understand planet formation processes, and (3) discuss future directions.

Sep 15 Rebecca Leane
host: Ali Kheirandish
Detecting Dark Matter in Stars and Planets

The theory describing dark matter remains completely unknown, and requires new search ideas to resolve its identity. It turns out that stars and planets can be ideal playgrounds to discover dark matter. I will review a range of dark matter searches using celestial objects, including exoplanets, solar-system planets, the Sun, and the Earth. I will discuss different search strategies, their opportunities and limitations, and the interplay of regimes where different celestial objects are optimal dark matter detectors.

Sep 22 Burkhard Militzer
U C Berkeley
host: Ashkan Salamat
Jupiter’s Interior Structure and the Origin of Saturn’s Ring

This talk will discuss the recent gravity measurements of Saturn and Jupiter by the Cassini and Juno spacecrafts. The interpretation of these measurements and the construction of interior models for these giant planets relies to a large degree on results from ab initio computer simulations of hydrogen, helium, and heavier elements at megabar pressures. Here we will review the uncertainties of the computed equations of state and identify conditions where the interior models are particularly sensitive to.

Then this talk will discuss recent findings of the Juno mission and explain why the unexpectedly low magnitudes of the gravity coefficients J4 and J6 imply that Jupiter has a dilute core at its center instead having of a traditional compact core that is composed to 100% of heavy elements.

Saturn stands out among the planets in our solar system for two reasons: It has a prominent set of rings and its spin axis is tilted by 27o. Both facts are difficult to reconcile with the well-established picture of planet formation, which assumes the planets emerged from a protoplanetary disk. Furthermore recent gravity measurements by the Cassini spacecraft implied an unexpected young age for Saturn’s rings of only ~100 million years, which rules out that the rings are primordial. Here we reconcile all these observations by constructing models for Saturn’s interior structure and by performing dynamical simulations of all relevant solar system objects. We present a dynamical scenario that explains how Saturn’s rings formed and how its spin axis was tilted.

Burkhard Militzer is professor of planetary science at the University of California, Berkeley. He is the director of the Center for Integrative Planetary Science. Since 2007, he has been on the faculty of the Department of Earth and Planetary Science and the Department of Astronomy. He has a background in condensed matter physics and received his PhD from the University of Urbana-Champaign in 2000. Today he works on understanding the interiors of giant planets with NASA missions Juno and Cassini. He also studies matter at extreme conditions with computer simulations.

Sep 29 Mohit Bhardwaj
host: Bing Zhang
Unveiling the Most Promising Formation Channel of FRBs Using Local Universe Bursts

The origin of fast radio bursts (FRBs) remains an enduring enigma in contemporary astronomy, even after 17 years since their serendipitous discovery. A plethora of models has been proposed to shed light on their origins, encompassing both cataclysmic and non-cataclysmic formation channels. Within the non-cataclysmic category, the debate persists on whether the majority of FRBs are promptly formed after the death of their progenitor main sequence star or arise from recycled compact objects.

In this talk, I leverage currently available observational data to address three pivotal questions:

  1. What are the prospects of detecting FRBs originating from proposed cataclysmic channels?
  2. Is there a single dominant FRB formation channel, governing these enigmatic bursts?
  3. If a dominant channel does exist, can it explain the observed diversity among FRB host galaxies and their local environments?

To address these probing questions, I use a sample of approximately two dozen local Universe FRBs (z < 0.1), many of which have been detected by the Canadian Hydrogen Intensity Mapping Experiment Fast Radio Burst (CHIME/FRB) Project. Our analysis provides compelling evidence that core collapse supernovae are likely the dominant formation channel of FRB progenitors. Finally, this finding has noteworthy implications for multi-wavelength follow-up studies of FRBs, which I also discuss in this talk.

Oct 6 Melinda Soares-Furtado
University of Wisconsin-Madison
host: Jason Steffen
Worlds & Suns in Context: The Role of Age and Environment

In this talk, I discuss the interactions between stellar hosts and planetary companions, including the ejection and ingestion of stellar companions. Drawing insights from stellar evolutionary models and observational survey data (photometric and spectroscopic), I present my team's latest discoveries as we seek to identify unambiguous ingestion-derived chemical tracers. Such tracers make it possible to identify engulfment events long after the original event has transpired and offer a critical opportunity to probe bulk planetary composition. Looking forward, infrared space-based missions will soon make it possible to investigate young, free-floating planets for the presence of satellites. These data will help to further constrain the formation pathways and dynamical histories of these starless worlds.

Oct 13 Luke Kelly
UC Berkeley
host: Carl Haster
Nanohertz Gravitational Waves: Exploring the Most Massive Black Holes in the Universe

Earlier this year NANOGrav, along with other pulsar timing arrays, announced strong evidence for a stochastic gravitational wave (GW) background at nanohertz frequencies. For decades, such a signal has been predicted from binaries of supermassive black holes (SMBHs). I will present NANOGrav’s recent data and our interpretation of the signal as produced by SMBH binaries. I will show that these GWs encode a wealth of new information about SMBH formation and evolution. Now, the race is on for the next expected measurements: detection of anisotropy in the GW background, and individual loud binaries. These measurements would confirm the origin of the GWs, provide a crucial testbed for the future LISA mission, and open a new multi-messenger window into the Universe.

Oct 20 Walter Drisdell
Lawrence Berkeley Lab
host: Craig Schwartz
Understanding Electrochemical CO2 Reduction With In Situ X-rays

Photoelectrochemical CO2 reduction is a promising clean energy strategy wherein solar energy is used to convert CO2 into storable liquid fuel. This addresses problems with both energy storage and the utilization of atmospheric CO2 to mitigate climate change. Unfortunately, current prototype devices suffer from limited durability that prevents stable generation of desired products. We present in situ and operando studies of Cu-based catalysts for CO2 reduction using synchrotron X-ray techniques including grazing incidence X-ray diffraction, X-ray spectroscopy, and small angle X-ray scattering. These provide insight into restructuring processes for the Cu-based catalysts, namely a preferential surface reconstruction towards (100) facets that does not occur in a CO2-free control experiment, and nanoscale agglomeration arising from competing particle migration and coalescence (PMC) and Ostwald ripening mechanisms. We also present new studies of the photo-driven side of the device, in collaboration with UNLV researchers. Using advanced nonlinear X-ray spectroscopy methods at X-ray free electron laser facilities, we are able to probe the interfacial electronic structure at solid-solid junctions that governs charge transport of photogenerated carriers. Following a demonstration of this sensitivity, we discuss future prospects for these measurements.

Oct 26 Mukul Bhattacharya
Penn State
host: Ali Kheirandish
Heavy element nucleosynthesis & energetic neutrinos from highly magnetized outflows

While nuclei lighter than iron are fused over the course of typical stellar evolution, almost half of the elements heavier than iron are created through the rapid neutron capture process (r-process). These nuclei are thought to be produced in magnetized outflows from neutron-rich explosive events including compact mergers and core-collapse supernovae. In this talk, I will discuss the potential of neutrino-driven winds from strongly magnetized and rapidly rotating protomagnetars as plausible sites for r-process nucleosynthesis. As heavy nuclei can eventually produce ultra-high energy cosmic rays, we examine the acceleration and survival conditions for these nuclei. We also explore the propagation of these jets within Wolf-Rayet stars and blue/red supergiants. In particular, we analyze the criteria for a successful jet breakout, maximum energy deposited into the cocoon and structural stability of these magnetized jets. We show that high-energy neutrinos can be produced for extended progenitors like blue/red supergiants and estimate the detectability of these neutrinos with IceCube-Gen2.

Oct 27 Nevada Day Recess

Nov 3 Jake Turner
Cornell University
host: Zhaohuan Zhu
The Ongoing Hunt to Detect the Radio Emissions of Exoplanets

One of the most important properties of exoplanets has not yet been directly detected despite decades of searching: the presence of a magnetic field. Observations of an exoplanet’s magnetic field would yield constraints on its planetary properties that are difficult to study, such as its interior structure, atmospheric escape and dynamics, and any star-planet interactions. The presence of magnetic fields on gas giants also affects the understanding of their origins and evolution. Additionally, magnetic fields may contribute to the habitability of terrestrial exoplanets. Observing planetary auroral radio emission is the most promising method to detect exoplanetary magnetic fields.

In this talk, I will present our recent study of the Tau Bootis exoplanetary system where we have the first possible detection of an exoplanet in the radio using LOFAR (Turner et al. 2021). Assuming the emission is from the planet, we derived a maximum surface polar magnetic field for tau Boo b between ~5-11 G. The magnetic field and emission strengths we derived are consistent with theoretical predictions, and if this detection is confirmed it will place important constraints on dynamo theory, comparative planetology, and exoplanetary science in general. Additionally, I will present the first results of an extensive multi-site follow-up campaign to confirm the radio detection of tau Boo b. Our first observing campaign consists of low-frequency radio data taken simultaneously from NenuFAR and LOFAR. Preliminary analysis of this data show no signs of emission. Therefore, the original signal may have been caused by an unknown systemic or we are observing variability in the planetary radio flux due to observing at different parts of the stellar magnetic cycle. Our second follow-up observing campaign is designed to test the latter conclusion. We have coordinated observations of the magnetic maps of the host star alongside many months of intensive radio monitoring by NenuFAR. Preliminary results on the second campaign will be presented. Finally, I will briefly highlight the promising landscape of studying exoplanetary magnetic fields in the coming decades with future ground- and space-based radio telescopes.

Nov 10 Veterans Day Recess

Nov 17

Nov 24 Thanksgiving Day Recess

Dec 1 Thayne Currie
University of Texas, San Antonio
host: Jason Steffen
Directly Imaging Extrasolar Planets with the Subaru Coronagraphic Extreme Adaptive Optics Project

The Subaru Coronagraphic Extreme Adaptive Optics Project (SCExAO) coupled to the CHARIS integral field spectrograph is the most advanced high-contrast imaging platform in the northern hemisphere. With SCExAO/CHARIS, we are carrying out a new search for imaging planets around nearby stars, using precision astrometry to determine which targets may host an exoplanet we can image. This survey has led to the first joint direct imaging + astrometric discovery of an exoplanet, enabled us to find exoplanets at a faster rate than before, and allowed us to study the planets’ atmospheres, weigh them, and track their orbits all at once. Finally, I describe SCExAO’s new upgrades, which will allow us to break new ground in exoplanet discovery and atmospheric characterization, help the project play a critical role in NASA’s future exoplanet programs, and demonstrate key technologies needed for imaging rocky planets around nearby stars with future extremely large telescopes like TMT and GMT.

Dec 8 Evan Scott
Nevada National Security Site
host: Tao Pang
Beam Physics Simulations for the Scorpius Accelerator

Scorpius is a next generation linear induction accelerator currently being designed by multiple national laboratories and will be installed at U1a, which is operated by the Nevada National Security Site. Scorpius is planned to deliver a 22.4 MeV, 1.4 kA electron beam up to four pulses at various pulse spacing and pulse widths. To help with the technical maturation of the project, several beam simulation codes have been implemented to estimate beam transport as well as tune the machine to minimize risk. Results will be shown of the current state of Scorpius beam transport using the XTR envelope code and the LSP particle-in-cell code. The simulations show that the current design of Scorpius is able to meet the high-level requirements, including delivering a beam with a less than 1000 mm-mrad emittance at the end of the accelerator for the four-pulse case at the desired beam spot size. Results of desorption in the injector and beam spill are also shown. Future planned simulations will be discussed.

Dec 15 Finals Week

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